A140973 - OEIS

%I #8 Sep 21 2013 21:08:22

%S 1,2,8,15,16,18,22,32,47,48,53,58,64,70,77,78,80,94,95,96,103,106,128,

%T 138,163,199,206,256,257,266,269,311,326,330,352,358,385,397,398,401,

%U 419,421,499,512,514,538,587,599,617,622,640,672,683,757,768,770,773

%N Numbers n such that arithmetic mean of squares of the first n tribonacci numbers is an integer.

%C Could arithmetic tribonacci mean (T(0)+...+T(n-1)) / n be an integer?

%C The arithmetic means are integers for the first 1, 2, 47, 53, 94, 103, 106 etc. tribonacci numbers. - _R. J. Mathar_, Aug 04 2008

%F n such that (T(0)^2+ T(1)^2+ ... + T(n-1)^2) / n is an integer. T(i) = i-th tribonacci number.

%Y Cf. A000073.

%Y Cf. A107239. - _R. J. Mathar_, Aug 04 2008

%K easy,nonn

%O 1,2

%A _Ctibor O. Zizka_, Jul 27 2008

%E Added 1 and 2 and extended from 32 on, _R. J. Mathar_, Aug 04 2008